A higher welding quality including better bead appearance and weld penetration shape, combined with reduced spatter, are increasingly in demand. Less generation of spatter, in particular, is needed to improve welding quality and minimize adhesion of spatter to jigs and tools, which in turn will increase maintenance efficiency and lead to a better working environment.
Analysis of the spatter generation mechanism, typically using high-speed cameras, has revealed that spatter generation timing can be divided into two main periods: a short-circuiting period and an arcing period. A conventional spatter reduction method during the arcing period is to output a high current or a rated voltage that causes a high current during a predetermined time immediately after arcing, following which, during the latter part of the arcing period, a low current is output. (See Patent Document 1.) Another known method is to detect a change in the voltage output waveform during the arcing period to predict short-circuiting, and to output a low current if a significant change is detected. (See Patent Document 2.)
In prior arts, the pushing up of a weld droplet toward the consumable electrode by arc force and the separation of a large spatter droplet are reduced by outputting a low current when the molten metal formed at the tip of the consumable electrode (hereafter referred to as the “droplet”) and the molten metal (hereafter referred to as the “weld pool”) formed on a welding workpiece cause a short-circuit. However, this generation of the short-circuit is unpredictable. Therefore, once the current output is reduced, the longer the time until the next short-circuit, the smaller the size of the area that is thermally affected by arcing. The result, if much time elapses, is the tendency to form an undesirably convex bead. This is unpreferrable bead appearance. In addition, the spatter reduction effect decreases when welding in the medium to high current range where short-circuits are less frequent.
In the method of predicting the generation of the short-circuit, the distance between the weld droplet and weld pool needs to be small. However, even if a signal indicating an imminent short-circuit is generated, an excessive arc force is applied between the droplet and weld pool at the time of detection because arc is concentrated. In this case, the droplet becomes separated in the form of a large spatter droplet, or is pushed up by the arc force. If the droplet is pushed up, it takes a long time for the droplet to extend downwards and cause the short-circuit, resulting in an excessively large droplet. This also causes a large spatter droplet.    Patent Document 1: Japanese Patent Unexamined Publication No. S59-202173.    Patent Document 2: Japanese Patent Unexamined Publication No. S60-145278.